Gas discharge lamp operating system

ABSTRACT

A gas discharge lamp operating system electric circuit is shown in schematic form with a saturable impedance in series with a capacitor and a discharge lamp. The system components are so selected that the system operates at or near third harmonic resonance during the warmup period, the operation gradually shifting close to resonance at supply current frequency during normal operation.

United States Patent 2,334,568 11/1943 315/243 2,482,894 9/1949 3l5/244X 2,487,092 11/1949 315/243X 2,588,858 3/1952 315/250 2,773,217 12/1956 315/243X 2,858,481 10/1958 315/173 2,470,460 5/1949 323/60 Primary Examiner.lohn Kominski Assistant ExaminerC. R. Campbell Attorney-Edward T. Connors ABSTRACT: A gas discharge lamp operating system electric circuit is shown in schematic form with a saturable impedance in series with a capacitor and a discharge lamp, The system components are so selected that the system operates at or near third harmonic resonance during the warmup period, the operation gradually shifting close to resonance at supply current frequency during normal operation.

[72] Inventor Maksymilian A. Michalski W0odside,N.Y. [211 Applv No. 673,837 [22] Filed Oct. 9, 1967 [45] Patented Jan.12,197l [73] Assignee Berke Photo Inc.

New York, NY.

[54] GAS DISCHARGE LAMP OPERATING SYSTEM 10 Claims, 11 Drawing Figs.

[52] U.S. Cl 315/282, 315/244, 315/289 [51} Int.Cl H05b 41/23, H05b 41/231, HOSb 41/04 [50] Field ofSearch 315/100U, 100H. 293, 294, 284, 282

[56] References Cited UNITED STATES PATENTS 2,333,499 11/1943 Warren 315/243X A? l M Jr saw u 0F. 4.

PATENTEDJANIZBYI INVENTO MKSYM/L Inn/4. 41/0/44 JK/ BY p 05% WW AT ORNEY GAS DBSCHARGE LAMP OPERATING SYSTEM The present invention relates to gas discharge lamps, and more particularly to an electric system' for operating gas discharge lamps containing mercury or mercury and other metal additives in the form of halides.

i-leretofore, gas discharge lamps have been operated using electric systems including ballasts connected in series with capacitances to provide regulated supplies for the discharge lamps. However, these types of ballast have been designed to limit the current to an amount at most lessthan 150 percent of the operating value for the discharge lamps even under starting conditions which are practically short circuit conditions.

A gas filled mercury lamp presents a very low impedance upon being ignited because the mercury is in liquid form and thus the resistance of the lamp depends only upon the type of the gas filling and upon the physical dimensions of the discharge lamps. As current is passed through the lamp it slowly warms up as the mercury is gradually vaporized. The gas pressure and impedance increase until a steady operating state is reached. in the event that the ballast design is such that the lamp current is kept constant, the warmup period of the lamp is quite long and several minutes may pass before the lamp light output is 100 percent. There are a number of applications where this limitation is a serious drawback. Particularly in graphic arts applications the warmup time of the lamp results in long exposure times which, of course, impede production and increase operating costs.

The present invention aims to overcome the foregoing difficulties by providing an electrical system for operating gas discharge lamps in which faster warmup time isachieved.

In accordance with the invention the electric system includes a saturable inductance in series with a capacitor and a discharge lamp. The system components are so selected that the system operates at or near third harmonic resonance during the warmup period, the operation gradually shifting to supply current at input source frequency resonance or near resonance during operation.

The system is advantageous in that a starting current of at least double normal current is provided during the warmup period which thereby lessens the time required for the lamp to reach operating temperature. ln addition, the operation at or near resonance acts as a stabilizing effect in maintaining practically constant light output and lamp voltage although there are variations in the input voltage.

Other objects and advantages of the invention will be apparent from the following description and from the accompanying drawings which show, by way of example, an embodiment of the invention.

in the drawings:

FIG. 1 is a schematic drawing of the circuit of an electric system in accordance with the invention.

FIG. 2 is a perspective drawing of an autotransformer showing shunts between the primary and secondary windings.

FIG. 3 shows a series of curves illustrating the performance characteristics of the electric system.-

FIG. 4 is a regulation curve of the electric system.

'FIGS. 5 and 6 show theoretical waveforms including the fundamental the third harmonic and the resultant waveforms with the third harmonic component in phase (FIG. 5) and leading by 90 (H6. 6).

FIGS. 7 through 9 show theoretical waveforms of line voltage, lamp current, and lamp voltage of systems with a capacitor in series with the discharge lamp (FIG. 7), a resistor in series with the discharge lamp (FIG. 8), and an inductor in series with the discharge lamp (FIG. 9).

H6. it) shows waveforms of the autotransformer voltage, the capacitor voltage, and the lamp voltage at the start of the warmup period for the discharge lamp.

FIG. it shows waveforms according to H0. 5 but taken after the warmup period has passed and during normal operatron.

Referring to the drawings there is shown in H6. 11 a schematic circuit 10 of an electric system in accordance with the invention. An alternating current source, Preferably of the order of 200 to 250 volts, is connected to the input terminals 11 and 12. An autotransforcmer 14' is provided'with a primary winding and a secondary winding 16. The secondary winding 116 is connected through a main capacitor 17 in series with secondary winding 19 of a starting trari forrher ZQwhich has its primary winding 21 supplied by a cofnv ti on ii'l starting circuit 22. The secondary winding 19 is es connc ct'ed to a discharge lamp 2 1 having terminals 25 and J being connected to terminal 25 while the term nal 16 is connected to the primary 15 of the autotransform 1 41 I The starting circuit 22 may be of any conve'nti onal type or may be as shown in US. Pat. No. 3,309,566 issued Mar. I4, 1967 to the applicant herein. In the operation of the starting circuit a series of high frequency pulses are produced in the starting circuit 22 and stepped up in voltage through the transformer 20 and superimposed on the alternating current supplied to the lamp 24. The starting pulse transformer 20 is of the ferrite core type, thereby being suitable for, passage of the high frequency pulses but presenting very low impedance to the passage of operating current. A bypass capacitor 27 is connected across the series connected secondary winding 19 of the starting transformer 20 and the lamp 24 to complete the circuit for the high frequency pulses of the starting circuit. The capacitor 27 is of low capacity and passes very little purrent at the operating frequency. v,

The autotransformer 14 is preferably of the type shown in FIG. 2 incorporating a core 30 which may comprise, a threelegged laminated core structure built up of El-shaped laminations and bar laminations with adjacent laminations being reversed to break the joints in the usual manne,r. The primary winding 15 and the secondary winding 16 are wound on the center leg 31. A pair of high reluctance magnetic shunts32 and 33 are interposed between the center legend the outer legs of the core 30 between the primary andsecondary windings 15 and 16. Air gaps are provided at,the ends of .the shunts, thereby making a loose coupling between the .primary and the secondary coils on the core. Althoughan autotransformer is preferred for use in the electric system in accordance with the invention alternative constructions might utilize a transformer having a loosely coupled secondary or a saturable inductance connected in series with the terminal voltage without any step up voltage means. Such a saturable reactor would provide high leakage reactance and act in a manner similar as the autotransformer described here. However, the autotransformer is considered the preferable construction because of lower material and construction cost.

ln the operation of the electric system in accordance with the invention the terminals 111 and 12 are connected to a source of alternating current preferably of standard 60 cycle frequency with a voltage of the order of 250 volts. The starting circuit is energized usually from the same alternating current source. Upon ignition of the discharge tube 24 by the starting circuit a current of at least twice normal operating current flows through the discharge lamp 24 thereby bringing it up to operating temperature at a rapid rate. The circuit constants are so selected and proportioned relative to the circuit constants of the discharge lamp 24 that the circuit resonates at or close to a harmonic frequency immediately upon ignition of the discharge lamp 24. The circuit constants are preferably arranged so that the operation is at the third harmonic. As the lamp warms up to operating temperature the circuit constants automatically adjust so that operation of the electric system gradually shifts to close to resonance at the supply frequency which is preferably 60 cycles, the leakage reactancc of the autotransformer cooperating with the capacitor t7 so that a regulating action is provided compensating to a large degree for variations in the voltage of the supply frequency.

in arriving at the parameters of the design of the system constants, the discharge lamp characteristics are viewed. The lamp resistance is practically linear in the operating range. The inductance of the secondary circuit of the autotransformer M and the capacitor l7 are selected with values such as to provide a near resonant condition for the operating conamount which may cause damage to the seals of the lamp.

During the warmup period the operation is at or near resonance at harmonic frequency, thereby the effective reduced capacitance of the capacitor 17 passes a higher than normal current. The inherent reactance of the autotransformer would tend to theoretically increase at the increased harmonic frequency. However the saturable effect of the greater than normal current during starting reduces the effective value of the inductance reactance under the harmonic condition.

Because of the great number of variables in the circuit it is apparent that the circuit constants may be more expeditiously arrived at by experiment rather than by calculation. For a typical metal additive lamp of 2,000 watts rating operating at an input voltage of 250 volts the normal operating current is about I amperes and the operating resistance is about 20 ohms. The inrush current should be limited to a maximum of 30 smperes in order that no damage be caused to the electrode seals. Upon ignition the resistance of the 2,000 watt lamp is only a fraction of an ohm. Therefore, the total impedsnce of the autotransformer secondary and of the capacitor 17 must be of the order of about 8 ohms.

Experiments are conducted with various values of capacitance and inductance and evaluated. For instance, for use with a 2,000 watt lamp, a capacitor of 20 mfd. would have a resctance of I42 ohms which would not permit enough initislcurrent to flow. A capacitor of I00 mfd. with a reactance of 26 ohms would pass too large a current. A capacitor of 80 :mfd. with a 60 cycle reactance' of 33 ohms was found to be practical with'the selected autotransformer because the initial current through the lamp was found to be less than 30 amperes. Under operating conditions the 33-ohm capacitive rcactsnce with the unsaturated reactance of the autotransformer together with the lamp resistance of 20 ohms resulted merls were made varying the relative number of turns on the primary and secondary and'varying the core and shunt area and the lengths of the air gaps. Ina working embodiment of the invention a core 30 was constructed in which the center leg 31 was 2% square inches in cross-sectional area with the outer legs 1% square inches in crosssectional area. The shunts 32 and 33 were 7/ l6 by l 3/32 inches in cross section, the end air gaps being about one-sixteenth of an inch. The shunts 32 and 33 were positioned between'the primary winding and the secondary winding 16. The primary winding 15 was wound with 304 turns of number 16. wire while the secondary 16 was wound with 176 turns of number 13 wire.

tained from calculations based upon the r.m.s. values of current and voltage during these times.

Performance characteristics curves of the electric system in accordance with the invention are shown in FIG. 3. It will be noted that lamp current curve 40 shows a starting current of about double normal. continuing generally at this magnitude 15 for about seconds, whereupon there is a rapid decrease in the current to normal operating value of about 10 amperes. The decrease in the current is related somewhat to the increase in the impedance of the lamp as it warms up to operating temperature and pressure.

20 Lamp wattage curve 41 initially is about 500 watts and generally follows the pattern of the current curve 40 and increases to slightly over 2,000 watts during operation. Curve 42 shows a voltage drop across the lamp of about 10 volts for approximately IO seconds, the lamp voltage then increasing rapidly for about the next seconds to reach its operating 30 wattage curve 41, the power factor rising rapidly during the 20 to 40 second period of operation.

It will be noted that between the 20 to 40 seconds period of operation there is a considerable change in the behavior of the lamp in respect to the current and voltage drawn thereby. The

current decreases while the lamp voltage increases together with the wattage of the lamp and the power factor of the circuit. This change of behavior does not depend entirely on the characteristics of the lamp but is brought about by the action of the other components of the circuit together with the lamp.

In prior designs this change has occurred gradually over a much greater period of time but with the increased starting currents of the present electric system the warming up period of the lamp is considerably reduced. The period of great change in the lamp characteristics is indicated between the 45 dashed vertical'lines 46 and 47 of FIG. 3, representing the period of operation from about 20 to about 40 seconds after start of operation.

The regulation of the lamp is shown by curve 48 (FIG. 4). It will be noted that the light variation is only 20 percent for an 50 input voltage variation of 50 volts, or a .4 percent change in the light output for each 1 percent voltage change.

As stated heretofore it is believed that the operation of the circuit in accordance with the invention depends upon operation at least close to resonance of the third harmonic for the The following table sets out the operating characteristics of warmup period, the operation generally shifting to at least the electrical system in accordance with the invention.

close resonance operation at cycles. Table I shows that the i i TABLE I The, Input Lamp Primary Capac- Trans- Lamp, Lamp, Light in Input, Volt, PI. m current current coll itor, former, volts watts foot watts ampere leading current volts volts candles inpu I. 24. 4. 410 410 20 500 30 900 6, 500 138 B. 0 23. 5 4. 95 415 410 20 500 48 900 5, 900 155 23. 5 23. 3 4. 95 413 412 20 500 900 5, 900 155 22. 2 Q. 0 4. 8 MB 410 35 600 850 1, 000 5, 600 178 12. 6 12. 5 4. 25 360 410 1, 620 1, 420 1, 800 3, 200 563 10.9 10.8 3. 8 340 400 190 1, 750 1, 880 1, 900 2,700 705 10.9 10. 8 3. 8 342 400 204 1, 950 2, 000 2, 100 2,700 750 10. l 10. 7 3. 8 342 400 206 2, 050 2, 000 2, 2, 700 10. 8 10. 7 3. B 342 400 206 2, 050 2, 000 2, 150 2, 700 800 10. 8 10. 7 3. 8 342 400 206 2, 050 2, 000 2, 150 2, 700 800 10. 8 10. 7 3. 8 340 400 206 2, 050 2, 000 2, 150 2, 700 800 10. B 10. 7 3. 8 340 400, 206 2, 050 2, 000 2, 150 2, 700 800 10. 8 10. 7 3. 8 340 400 206 2, 050 2,000 2, 150 2,700 800 10. 8 10. 7 3. 8 340 400 206 2, 050 2, 000 2, 150 2, 700 800 Table II sets out the respective values of the impedances of the secondary inductance and of the capacitor under starting and operating conditions. These impedance values were obcapacitor voltage and the transformer voltage are identical in value at start therefore providing evidence of a resonant con- 75 dition.

Also, the calculations of the inductive and capacitive impedance as set out in table II made from the data of table I show that the two impedance values are identical. The capacitive reactance for 80 mfd. at 60 cycles equals for 60 cycles=33 ohms.

which compares favorably with the figure of 3 1 .8 ohms shown above. When the values are calculated for initial starting conditions and substituted for 180 cycles the capacitive reactance is calculated at 11 ohms. The specific value of 17 ohms obtained in the practical circuit as compared with the l 1 ohms calculated for the third harmonic just mentioned shows that there is some phase shift effect or waveform distortion.

Under operating conditions the capacitor voltage is lower by approximately percent than the transformer voltage indicating that the circuit is not quite in resonance which is advantageous because if the circuit were in resonance unstable conditions would occur. During warmup the importance of stable operation is not so important.

It will be noted that upon ignition the lamp current is 24 amperes dropping off to 10.7 amperes for operation. Thus the starting current is 2.24 times operating current. Of course if the seals permitted a larger starting current, a faster warmup could be achieved. The circuit may be readily adjusted to provide a larger starting current by increasing the capacitance and decreasing the inductance.

The gain in warmup time is appreciable when compared with standard available ballast. Under the same conditions, a gain of 3 to 4 times can be achieved. For example a 2,000-watt metal halide lamp reaches 75 percent of its output in 30 seconds and 100 percent output in 45 seconds (curve 41). The same lamp operated with a standard ballast reaches 75 percent output in 90 seconds and 100 percent output in 2 /2 to 3 minutes. Also, comparable savings in material costs in copper and laminations are in the range of 30 to 40 percent. Power factor obtained with the new type is .8 while the conventional ballast types usually operate at .6-power factor.

Further explanation of the operation of the circuit may be had by comparing theoretical waveforms with waveforms taken during the operation of the circuit.

In FIGS. 5 and 6 there are shown theoretical waveforms copied from textbooks for comparison with the actual wavefonns taken during operation of a system in accordance with the invention and illustrating the effect on the shape of a waveform with harmonic components. Waveform 50 of FIG. 5 is the resultant of a fundamental 51 and a third harmonic 52 in which the third harmonic is in phase with the fundamental. In FIG. 6 the waveform 54 is the resultant of the fundamental waveform 55 and a third harmonic waveform 56 but in which the third harmonic waveform 56 leads the fundamental waveform 55 by 90.

Other theoretical waveforms are shown in FIGS. 7--9 and illustrate the effects when a discharge lamp is alternatively connected in series with a capacitor, a resistor, or an inductance. Waveform 59 of FIG. 7 shows a supply voltage waveform. Waveform 60 shows the discharge lamp or tube voltage while waveform 61 shows the waveform of the lamp current. The waveforms 59 to 61 illustrate operation with a capacitor series connected with the discharge lamp.

Waveform 62 of FIG. 8 shows the supply voltage and waveform 64 the discharge lamp or tube voltage, while waveform 65 is of the lamp current. The waveforms 62 to 65 illustrate operation with a resistor series connected with the discharge lamp.

In FIG. 9 waveform 66 shows the supply voltage waveform. Waveform 67 shows the discharge lamp or tube voltage while waveform 69 shows the lamp current. The waveforms 66 to 69 illustrate operation with an inductor series connected with the discharge lamp.

In FIG. 10 the waveforms shown were taken at the start of the warmup period for the discharge lamp 24. Waveform 70 was taken across the autotransformer 14 including the series connected primary l5 and the secondary l6. Waveform 7] shows the voltage across the main capacitor 17 and waveform 72 shows the voltage across the discharge lamp 24.

It will be noted that at the start of the warmup period the autotransformer voltage waveform includes a relatively small harmonic effect, while the capacitor voltage waveform 7 I and the discharge lamp voltage waveform 72 clearly show leading third harmonic effects. The third harmonic effect is apparently caused by the partial saturation of the autotransformer due to its regulating action.

In FIG. 11 the waveforms shown were taken at the end of the warmup period for the discharge lamp 24 and during normal operation thereof. Waveform 74 corresponds to waveform 70 of FIG. 10 and shows the voltage across the series connected primary I5 and secondary 16 of the autotransformer 14. The capacitor voltage is shown as waveform 75 and the lamp voltage as waveform 76. The absence of harmonic components in the capacitor waveform 75 and the decreased harmonic effect in the discharge lamp waveform 76 will be noted. Also note the increased harmonic effect in the autotransformer voltage waveform 74.

In FIG. 11 waveforms 79 and 80 show respectively the starting and operating currents in the circuit.

Thus it will be seen that an electric system has been disclosed which advantageously operates at or near resonance during the warmup period thereby supplying the discharge lamp with increases current to bring the lamp quickly to operating temperature. Thereafter the system operates close to resonance thereby providing a regulating action so that the light output of the discharge lamp remains practically constant during the usual line voltage variations.

While the invention has been described and illustrated with reference to a specific embodiment thereof it will be understood that other embodiments may be resorted to without departing from the invention. Therefore, the form of the invention set out above should be considered as illustrative and not as limiting the scope of the following claims.

I claim:

1. An electric system for use with an alternating current source comprising a saturable transformer, a capacitor, and a gas discharge lamp connected in a series circuit, the lamp when initially ignited having low impedance, the lamp impedance increasing as the lamp is warmed up to operating temperature, the respective values of the impedances of the saturable transformer, the capacitor, and the lamp being such that a harmonic component is generated in said series circuit upon ignition of said lamp, said circuit operating at least close to resonance at said harmonic frequency during the warmup period of said lamp, the circuit constants being such that operation of said circuit gradually shifts to at least close to resonance at supply frequency as said lamp reaches operating temperature, specifically the saturable transformer having constants such that it has a partially saturated primary during the starting phase using the resonance of the third harmonic current, the constants of the saturable transformer such that its primary gradually unsaturates as the lamp warms up using supply frequency resonance, whereby during the operation at close to harmonic frequency the effective reduced capacitive reactance passes a higher than normal current to flow through said lamp for a rapid warmup thereof and as said harmonic component decreases the effective increased capacitive reactance reduces the current flow to normal and at the same time the operation at least close to resonance at supply frequency provides regulating action in the event of variations in said supply frequency.

2. An electric system according to claim 1 in which said harmonic frequency is the third.

3. An electric system according to claim 1 in which said saturable inductance is an autotransformer with a high reluctance magnetic shunt between the primary and secondary coils.

4 An electric system according to claim 1 in which the voltage drops across said saturable inductance and said capacitor are practically equal during said harmonic operation.

5. An electric system according to claim 1 in which the voltage drop across said saturable inductance is at least 75 percent of the voltage drop across said capacitor at said operation at least close to supply frequency resonance.

6. An electric system according to claim 1 in which the r.m.s. value of the lamp current at said operation upon ignition of said lamp is at least twice the r.m.s. value of the normal operating current. v

7. An electric system according to claim 1 in which said harmonic frequency is the third and said saturable inductance is an autotransformer with a high reluctance magnetic shunt between the primary and secondary coils.

8. An electric system according to claim 1 in which said harmonic frequency is the third, said saturable inductance is an auto transformer with a high reluctance magnetic shunt between the primary and secondary coils, and the voltage drops across said saturable inductance and saidcapacitor are practically equal during said harmonic operation.

9. An electric system according to claim 1 in which said harmonic frequency is the third, said saturable inductance is an autotransformer with a high reluctance magnetic shunt between the primary and secondary coils, and the r.m.s. value of the lamp current at said operation upon ignition of said lamp is at least twice the r.m.s. value of the normal operating current.

10. An electric system according to claim 1 in which said harmonic frequency is the third said saturable inductance is an autotransformer with a high reluctance magnetic shunt between the primary and secondary coils, the voltage drop across said saturable inductance is at least 75 percent of the voltage drop across said capacitor at said operation at least close to supply frequency resonance, and the r.m.s. value of the lamp current at said operation upon ignition of said lamp is at least twice the r.m.s. value of the normal operating current. 

1. An electric system for use with an alternating current source comprising a saturable transformer, a capacitor, and a gas discharge lamp connected in a series circuit, the lamp when initially ignited having low impedance, the lamp impedance increasing as the lamp is warmed up to operating temperature, the respective values of the impedances of the saturable transformer, the capacitor, and the lamp being such that a harmonic component is generated in said series circuit upon ignition of said lamp, said circuit operating at least close to resonance at said harmonic frequency during the warmup period of said lamp, the circuit constants being such that operation of said circuit gradually shifts to at least close to resonance at supply frequency as said lamp reaches operating temperature, specifically the saturable transformer having constants such that it has a partially saturated primary during the starting phase using the resonance of the third harmonic current, the constants of the saturable transformer such that its primary gradually unsaturates as the lamp warms up using supply frequency resonance, whereby during the operation at close to harmonic frequency the effective reduced capacitive reactance passes a higher than normal current to flow through said lamp for a rapid warmup thereof and as said harmonic component decreases the effective increased capacitive reactance reduces the current flow to normal and at the same time the operation at least close to resonance at supply frequency provides regulating action in the eVent of variations in said supply frequency.
 2. An electric system according to claim 1 in which said harmonic frequency is the third.
 3. An electric system according to claim 1 in which said saturable inductance is an autotransformer with a high reluctance magnetic shunt between the primary and secondary coils.
 4. An electric system according to claim 1 in which the voltage drops across said saturable inductance and said capacitor are practically equal during said harmonic operation.
 5. An electric system according to claim 1 in which the voltage drop across said saturable inductance is at least 75 percent of the voltage drop across said capacitor at said operation at least close to supply frequency resonance.
 6. An electric system according to claim 1 in which the r.m.s. value of the lamp current at said operation upon ignition of said lamp is at least twice the r.m.s. value of the normal operating current.
 7. An electric system according to claim 1 in which said harmonic frequency is the third, and said saturable inductance is an autotransformer with a high reluctance magnetic shunt between the primary and secondary coils.
 8. An electric system according to claim 1 in which said harmonic frequency is the third, said saturable inductance is an auto transformer with a high reluctance magnetic shunt between the primary and secondary coils, and the voltage drops across said saturable inductance and said capacitor are practically equal during said harmonic operation.
 9. An electric system according to claim 1 in which said harmonic frequency is the third, said saturable inductance is an autotransformer with a high reluctance magnetic shunt between the primary and secondary coils, and the r.m.s. value of the lamp current at said operation upon ignition of said lamp is at least twice the r.m.s. value of the normal operating current.
 10. An electric system according to claim 1 in which said harmonic frequency is the third, said saturable inductance is an autotransformer with a high reluctance magnetic shunt between the primary and secondary coils, the voltage drop across said saturable inductance is at least 75 percent of the voltage drop across said capacitor at said operation at least close to supply frequency resonance, and the r.m.s. value of the lamp current at said operation upon ignition of said lamp is at least twice the r.m.s. value of the normal operating current. 